FIG. 1 illustrates an example of an electrostatic discharge (ESD) protection circuit according to the related art.
In FIG. 1, reference numeral 101 represents a diode for ESD protection, reference numeral 102 represents an input pad of an integrated circuit (IC), and reference numeral 103 represents an output pad of the integrated circuit (IC). Also, reference numeral 104 represents a line connected to a pad for a power supply voltage that supplies a power supply voltage to a circuit, and reference numeral 105 represents a line connected to a pad for grounding the circuit.
Reference numeral 106 represents a circuit that allows a current of static electricity generated in the input pad 102 to flow out through the power supply voltage line 104 or the ground line 105, and reference numeral 107 represents a circuit that allows the current of static electricity generated in the output pad 103 to flow out through the power supply voltage line 104 or the ground line 105.
Reference numeral 108 represents a power clamp circuit that allows the current of static electricity to flow between the power supply voltage line 104 and the ground line 105. Reference numeral 109 represents an internal circuit having low endurance from static electricity. A circuit consisting of ESD protection elements including a diode so as to protect the internal circuit having low endurance from static electricity, as illustrated in FIG. 1, is referred to as an ESD protection network.
FIG. 2 illustrates an example in which the ESD protection network of FIG. 1 operates. In FIG. 2, the flow of the current of static electricity when static electricity is generated in the input pad 102 and flows out to the output pad 103, is indicated by reference numeral 201. In this case, static electricity generated in the input pad 102 flows in the power clamp circuit 108 through the power supply voltage line 104 via the circuit 106, and the current of static electricity flows out to the output pad 103 via the circuit 107. As illustrated in FIG. 2, the current of static electricity bypasses the internal circuit with low endurance from static electricity so as to safely flow out to the output pad 103.
FIG. 3 illustrates another example of an operation of the ESD protection network of FIG. 1. In FIG. 3, the flow of the current of static electricity when static electricity is generated in a pad for grounding 301 and flows out to a pad for a power supply voltage 302, is indicated by reference numeral 303. As in reference numeral 303, the current of static electricity starts from the pad for grounding 301 and flows out to the pad for the power supply voltage 302 via the circuit 107. Even in this case, as illustrated in FIG. 2, the ESD network operates in such a way that the current of static electricity bypasses the internal circuit with low endurance from static electricity.
If static electricity generated in the pad for grounding 301 flows out to the pad for the power supply voltage 302, as illustrated in FIG. 3, the current of static electricity should pass through two diodes of the ESD protection circuit 107. In general, when the current of static electricity passes through the ESD protection element, such as a diode, power consumption occurs due to parasitic resistances of the ESD protection element. Power consumed in this way is transformed to heat. If transformed heat rises to a higher temperature than a melting point of the ESD protection element, the ESD protection element is destroyed, and the whole ESD protection circuit 107 is destroyed by static electricity and as such, a desired function cannot be performed any more. Thus, it is significant to configure the ESD protection network to pass through a minimum ESD protection element until the current of static electricity flows out from the circuit.
FIG. 4 illustrates an example in which an ESD protection network is configured in such a way that, when the current of static electricity is generated, as illustrated in FIG. 3, the current of static electricity can pass through one ESD protection element. In FIG. 4, a P-type semiconductor of a diode 401 is connected to the ground line 105, and an N-type semiconductor of the diode is connected to the power supply voltage line 104. In this case, like in FIG. 3, when static electricity generated in the pad for grounding 301 should flow out to the pad for the power supply voltage 302, unlike in FIG. 3, the current of static electricity flows through the diode 401. That is, the number of diodes through which the current of static electricity passes through, of FIG. 4 is reduced by one compared to FIG. 3.
Thus, when the same current of static electricity is applied to the circuits of FIGS. 3 and 4, in FIG. 3, the current of static electricity should pass through two diodes, and in FIG. 4, the current of static electricity should pass through one diode. Thus, ideally, in FIG. 4, parasitic resistances caused by the diode are reduced by half compared to FIG. 3. Thus, when the same current of static electricity flows through the circuits of FIGS. 3 and 4, in FIG. 4, power consumption caused by the current of static electricity is reduced by half compared to FIG. 3. Thus, the increase in a temperature of the circuit of FIG. 4 is reduced compared to FIG. 3. As a result, the ESD protection network of FIG. 4 has a higher endurance from static electricity than the ESD protection network of FIG. 3.
FIGS. 5A and 5B illustrate an ESD protection diode according to the related art. FIG. 5A shows the layout of the ESD protection diode according to the related art, and FIG. 5B shows a symbol thereof.
As illustrated in FIG. 5A, the ESD protection diode is configured as a combination of an N-type semiconductor 501 and a P-type semiconductor 502. In actuality, the N-type semiconductor 501 and the P-type semiconductor 502 have uniform resistances, and additionally, parasitic resistances exist in a junction of the N-type semiconductor 501 and the P-type semiconductor 502. If the current of static electricity passes through the ESD protection diode, due to the parasitic resistances in the diode, voltage drop occurs in both ends of the ESD protection diode. Due to the voltage drop and the current of static electricity, power of the ESD protection diode is consumed, and the temperature of the PN junction rises.
Although the ESD protection network of FIG. 4 has a higher endurance from static electricity than the ESD protection network of FIG. 3, the ESD protection network of FIG. 3 is generally preferable. This is because the diode 401 should be additionally connected to the ESD protection network of FIG. 3 so as to configure the ESD protection network of FIG. 4.
In a present integrated circuit (IC), the size of a circuit directly relates to production cost. The use of an additional element in the circuit causes an increase in the size of the circuit, which causes an increase in production cost. Thus, although the ESD protection network of FIG. 4 has a higher endurance from static electricity than the ESD protection network of FIG. 3, production cost for the circuit may increase compared to FIG. 3.